1. Field of the Invention
The present invention relates to a nitride-based semiconductor laser device and a method of manufacturing the same, and more particularly, it relates to a nitride-based semiconductor laser device provided with an optical waveguide and a method of manufacturing the same.
2. Description of the Background Art
In general, a light-emitting device made of a nitride-based material such as gallium nitride (GaN) has been put into practice as a 405 nm blue-violet semiconductor laser (LD) as a light source for recording/playing employed as a DVD system. A semiconductor laser device emitting blue or green light, employing a nitride-based material has been developed. Considering that luminous efficiency is reduced due to an influence of large piezoelectric field in a light-emitting device formed on a polar face ((0001) plane) of a GaN substrate, a nitride-based semiconductor laser device formed with a light-emitting device layer on a nonpolar face ((1-100) plane or (11-20) plane) of a GaN substrate has been proposed. Such a nitride-based semiconductor laser device is disclosed in Japanese Patent Laying-Open No. 8-213692 and Japanese Journal of Applied Physics Vol. 46, No. 9, 2007, pp. L187-L189.
The nitride-based semiconductor laser device disclosed in the aforementioned Japanese Patent Laying-Open No. 8-213692 and Japanese Journal of Applied Physics Vol. 46, No. 9, 2007, pp. L187-L189 has a striped ridge as an optical waveguide. A resist is employed as a mask for dry etching such as reactive ion etching (RIE), or inductively coupled plasma (ICP) etching, thereby forming this ridge.
When the ridge is formed by dry etching as in the nitride-based semiconductor laser device disclosed in the aforementioned Japanese Patent Laying-Open No. 8-213692 and Japanese Journal of Applied Physics Vol. 46, No. 9, 2007, pp. L187-L189, however, the side walls of the ridge are not sufficiently flattened. When the side walls of the ridge are not sufficiently flattened, a horizontal transverse mode is disadvantageously unstable. When the horizontal transverse mode is unstable, a far-field pattern (FFP) is likely to be asymmetric and kink (nonlinearity) in I-L characteristics disadvantageously occurs.